JP-A 3-248551 representing prior art technology provides an electronic component obtained, as shown in FIGS. 1 and 2, by placing a semiconductor chip 4′ on the upper surface of a tip end of one lead terminal 2′ of at least a pair of left and right lead terminals 2′, 3′, electrically connecting the semiconductor chip 4′ and the upper surface of a tip end of the other lead terminal 3′ by wire bonding with a fine metal wire 5′, and packaging the portions of the semiconductor chip 4′ and metal wire 5′ with a molded part 6′ from a thermosetting synthetic resin so that the lead terminals 2′, 3′ project outwardly along a bottom surface 6a′ of the molded part 6′.
Further, when the package type electronic component 1 of the above-described configuration is manufactured by the conventional process, a well-known method is employed by which, as shown in FIG. 3, a lead frame A′ punched out from a thin metal sheet is used, the aforementioned pair of lead terminals 2′, 3′ are formed inwardly so as to face each other in the lead frame A′, the tip ends of the two lead terminals 2′, 3′ are stepwise bent, then the semiconductor chip 4′ is placed on the upper surface of the tip end of one lead terminal 2′, the semiconductor chip 4′ and the upper surface of the distant end of the other lead terminal 3′ are electrically connected by wire bonding with a fine metal wire 5′, then a finished product of the electronic component 1′ is obtained by molding the molded part 6′ for packaging the entire structure, and each electronic component 1′ in the lead frame A′ is then cut and separated form the lead frame A′ by cutting with a fixed punch C1′ and a punch C2′ movable in the vertical direction at the positions of cutting lines B1′, B2′ in each lead terminal 2′, 3′ as shown in FIG. 4.
The above-described package-type electronic component 1′ is cut and separated from the lead frame A′, as described hereinabove, by cutting with the fixed punch C1′ and punch C2′ movable in the vertical direction at the positions at cutting lines B1′, B2′ in each lead terminal 2′, 3′. As a result, on the cutting faces 2e′, 3e′ of the lead terminals 2′, 3′, as shown in FIG. 1, cutting burrs D1, D2 produced by cutting are formed so as to project downwardly from rear surfaces 2b′, 3b′ of the front surfaces (upper surfaces) 2a′, 3a′ and rear surfaces (lower surfaces) 2b′, 3b′ in the lead terminals 2′, 3′, and those cutting burrs cause the following inconveniences. Thus, the cutting burrs D1, D2 hinder bending of the lead terminals 2′, 3′, hinder soldering of the lead terminals 2′, 3′ to a circuit board or the like, or degrade heat dissipation from the electronic component 1 to the circuit board or the like because the lead terminals 2′, 3′ are lifted by the cutting burrs D1, D2 from the circuit board.
In addition, when cutting is conducted with the fixed punch C1′ and punch C2′ movable in the vertical direction, a large cutting force is necessary and strong impacts act upon the lead terminals 2′, 3′. As a result, the lead terminals 2′, 3′ are separated from the molded part 6′ and tight sealing thereof with the molded part 6′ is degraded.
The above-described problems of inhibited soldering and degraded heat dissipation become especially significant in the case of electronic component 1′ of the above-described type wherein the lead terminals 2′, 3′ projecting from the molded part 6′extend outwardly along the bottom surface 6a′ of the molded part 6′.
Accordingly, as described in Japanese Patent Application Laid-open No. 5-55436 representing prior art technology close to the present invention, as shown in FIG. 5, notches 7′, 8′ for cutting are recess indented, before cutting the lead terminals 2′, 3′, in the lower surfaces 2b′, 3b′ of the lead terminals 2′, 3′, for example, by punching with a punch, so that the notches 7′, 8′ reach the longitudinal side surfaces 2c′, 2d′, 3c′, 3d′ on the left and right sides in the lead terminals 2′, 3′, that is, cross the entire width of the lead terminals 2′, 3′, and the lead terminals 2′, 3′ are cut with the fixed punch C1′ and punch C2′ movable in the vertical direction along the cutting lines B1′, B2′ at the positions of those notches 7′, 8′, thereby preventing the cutting burrs D1, D2 originating during cutting from projecting downward from the lower surfaces 2b′, 3b′ of the lead terminals 2′, 3′ and reducing the cutting force required for cutting.
However, the following problems are associated with the method by which the notches 7′, 8′ for cutting are recess indented in the lower surfaces 2b, 3b′ of the lead terminals 2′, 3′ so as to cross the entire width of the lead terminals 2′, 3′ and the lead terminals 2′, 3′ are cut at the positions of the notches 7′, 8′.
Thus, when indenting the notches 7′, 8′ for cutting is conducted after molding the molded part 6′, strong impacts occurring when the notches 7′, 8′ are molded act upon the lead terminals 2′, 3′ and the lead terminals 2′, 3′ are separated from the molded part 6′, thereby creating a high risk of degrading the tight sealing of the lead terminals 2′, 3′ with the molded part 6′.
On the other hand, the advantage of indenting the notches 7′, 8′ for cutting before molding the molded part 6′ is in that tight sealing of the lead terminals 2′, 3′ with the molded part 6′ can be ensured and a solder plated layer can be formed on the inner surface of the notches 7′, 8′, but the drawback of this method is that when the molded part 6′ is formed, part of the molten synthetic resin penetrates into the notches 7′, 8′ and is cured therein, thereby producing burrs of synthetic resin in a packed state inside the notches 7′, 8′.
When the lead terminals 2′, 3′ are cut at the positions of notches 7′, 8′ in this state, damage of the cutting knives is increased, a smooth cutting face cannot be obtained, and impacts acting upon the lead terminals during cutting are not reduced. As a result, a difficult deburring operation has to be implemented with respect to the lead terminals 2′, 3′ after molding the molded part 6′ and before cutting the lead terminals 2′, 3′ to remove the burrs of synthetic resin that penetrated into the notches 7′, 8′ and was cured therein. This troublesome operation greatly increases the cost. Another problem is that the deburring is sometimes impossible in small semiconductor devices, that is, with thin lead terminals.
It is a technological object of the present invention to provide a cutting method that is free from the above-described problems.